WARNING: Long rant!
There are two real things that I have a major problem with, concerning Macs.
I use Macs quite often at work, not as often as I used to, thank goodness, but still keep up with things on the platform. Overall, things in the Mac world aren't all that bad. The hardware is usually pretty good, design wise. OK, there are exceptions (the eMac is both the ugliest computer and also, thanks to its alarmingly smooth curves, astonishingly difficult to pick up and hold without it popping through your arms like a greased pig). I can't say the internal components are anything special. If anything, where I work, they have higher failure rates than the big-brand PC workstations. However, the design is pretty good.
OS X is, as Ross says, very polished. There are definitely a few wows when using OS X. I certainly have a few head-scratches with it as well. I maintain the Dock is really stupid. You can get some humdingers with it, like having two identical icons on the dock, one being a shortcut, the other a loaded instance, and other things which don't make sense. And the bouncing icons are infinitely irritating. However, it is now a pretty decent OS, certainly over OS 7/8/9. Its certainly come a long way since OS X was first released, which was a buggy, unfinished mess.
I also have no problems with their keyboards, mice or any other hardware (except Zen Sleek > iPod!).
No, the two problems I have with Macs are, firstly, Macs are fine and easy to use, as long as, and ONLY as long as, you do things absolutely the way Apple perscribe. And no going off the beaten path. Ever. And this doesn't just apply to being a user, but to being a developer, a sys admin, whatever. If you are a developer, you'd better get to learn Objective C. "Objective what?" I hear 99% of the development world cry. Apple's way or the high way, son. You try and develop any other way and its again, fighting the system. Scripting is just as bad. Script the Apple Script way or face dropping into the murky world of bash scripts where scripting OS X functionality is a shadowy game of chance, where OS X will just decide to override what you are doing for fun.
Being a sys admin is no fun either. Again, use what Apple tells you to use or get lost. No fun, when half of Apple's tools (Remote Desktop, etc) are pretty awful. And its not like they are helping you in your environment. Many people integrated OS 9 into Novell environments with Prosoft Engineering's client. Along comes OS X, and bam, they sliced this off. Eventually, Prosoft came out with a client (unfortunately, AFTER Apple had there little wheeze to prevent OS 9 being installed on new hardware) but I think, even to this day, it can't do some complicated stuff, like, erm, print to many Novell printer setups. Oh, and there is the Active Directory compatibility in OS X, which is what could best be described as "erratic".
The other problem. Well, let's put it this way. In the UK this christmas, there has been a best selling book called "Is It Just Me Or Is Everything Sh*t?". Its a very hilarious encyclopedia of everything that is annoying in modern society from Live8 to Coldplay to Airport Parking. The letter M starts with "Mac Junkies".
As you might imagine, the entry discuss those irritating people who go on and on and on about Macs being better than PCs when most people don't really give a flying one. Using a Mac over a PC does not mean you are sticking it to Bill Gates or "The Man", it does not mean you are Enlightened, it does not mean you are part of some cult. To a man, every Mac zealot I have come across is vastly more irritating than any Linux, Windows, Unix or Open Source fanboy I have met. Reason? For example, A Linux zealot will praise Gnome but slag off KDE. A Linux zealot will concede that maybe some of the software on the platform isn't absolutely perfect. Even Beer does! For a Mac fanboy to slag off ANYTHING about Macs is almost seen as treasonous. It goes over the line with the Converter brigade though. Those Mac zealots who proudly boast about converting friends, family, colleagues, strangers. Get people to try Firefox to try and covert them to that is a small free download, get people to try Linux is just downloading a free Live CD. No, these people pipe up when people ask for advice on the spec of their new PC: "oh you should get a Mac, and you wont have any of the problems Windows users have", and the poor people who asked for advice go out, spend a grand or more on a Mac and then, too often, get home to find it doesn't run any of their software and is not what they wanted. Trust me, working at a University, I'd heard similar stories to this too often from poor misguided about-to-start-University kids.
Still, this person can go away smug in that he has has converted someone to Mac, thinking he's special, when really, all his ilk has become is an example of something that a million plus readers will see is "Sh*t"